It depends on your campaign and how you want to run it. Some people like a looser, more
RPG-styled MH campaign. In which case, don't sweat it. Others like a tighter, more competitive campaign. If you or the guys in your campaign trend toward the latter, I think my advice would just be to use the alternate setting warbands at your own risk.
Ostlanders should be fine...
IMO they're kinda middling among human mercs. I've never seen
DE in action over an entire campaign, but
IIRC the Lustria creators admitted that the Lustrian warbands tend to be a little stronger than the rulebook warbands. So I'd say it's your call. If they end up dominating, you can always ban them in campaign #2.
The player is still the key factor. Shadow Warriors can get disgusting, but you can also play them poorly and lose a lot.